I work in California and recently my employer has told us that our overnight shifts are not subject to overtime laws. According to them if we start at 6 PM and finish at 6AM, the wage is computed at regular for both days since they fall into two different days. Is this correct? What is the definition of a shift?

A company can set any 24 hour period it wishes for an employee's work day. However, it can not arbitrarily change it in order to avoid paying overtime. In the case of a shift from 6PM-6AM, if the workday is defined as midnight to midnight, then this is treated as 6 hours in day 1 and 6 hours in day 2. However, if you go to work on day 2 for another shift of 6PM-6AM, then all hours after 8PM must be paid as overtime.

The end result is that it is slightly in the employer's advantage to do this. However, if you work 2 or more consecutive days in the week, you must be paid overtime for the hours worked over 8 in a day. If you work 5 or more such shifts in a week, it makes no difference because of the requirement to pay over 40 hours in a week.

The term "shift" is defined in the work orders as:

"Shift" means designated hours of work by an employee, with a designated beginning time and quitting time.

This does not help your case because no law requires overtime after 8 hours in a shift. It is after 8 hours in a workday.

This does seem a little odd, but it is what the law allows.